The present invention relates to improvements in apparatus for operating clutches. More specifically, the invention relates to improvements in apparatus which can be utilized with advantage as a means for operating friction clutches of the type utilized in power trains between engines or other prime movers, and variable-speed transmissions in motor vehicles.
A clutch of the type suitable to be operated by the apparatus of the present invention normally comprises operating means, such as a diaphragm spring, which changes its orientation and/or position during engagement and disengagement of the clutch. Conventional operating apparatus employ a carrier which is or which can be installed on the case of the transmission and mounts at least one support. The latter carries an actuator which is rotatable about and movable in the direction of the common axis of the pressure plate, counterpressure plate and housing of the clutch. The actuator serves to displace the operating means of the clutch by way of a bearing and the support prevents the bearing from leaving the position it assumes when the clutch is engaged. The means for moving the actuator relative to the support in the axial direction of the clutch includes a system of cams or ramps which cause the actuator to move axially of the clutch in response to rotation of the actuator relative to the support. Reference may be had, for example, to published French patent application No. A 2 658 763.
A drawback of presently known clutch operating apparatus, including that disclosed in the aforementioned published French patent application, is that they are rather complex (because they comprise a large number of parts), prone to malfunction and expensive. Furthermore, the assembly of the parts is a highly complex and time consuming operation.
Another drawback of heretofore known clutch operating apparatus is that, if the clutch is provided with a mechanism which is to compensate for wear upon the friction linings of the clutch disc and/or upon the friction surfaces of the pressure plate and counterpressure plate, the bearing or bearings of the operating apparatus are no longer capable of moving the operating means of the clutch to one and the same position relative the pressure plate and counterpressure plate as the wear upon the friction linings and certain other components of the clutch increases, i.e., in response to progressing axial shifting of the pressure plate toward the counterpressure plate and attendant change of orientation of the operating means of the clutch, such as the aforementioned clutch spring. The problem is particularly serious if the force-transmitting connection between the clutch pedal in a motor vehicle and the bearing of the clutch operating apparatus comprises a linkage or a bowden wire. The tolerances in the force transmitting connection are compounded by tolerances which develop in such connection as a result of progressing wear upon the friction linings of the clutch disc and the friction surfaces of neighboring parts. In other words, the play which develops between the clutch pedal and the bearing or bearings of the clutch operating apparatus due to progressing wear upon the friction linings is not compensated for by heretofore known clutch operating apparatus so that the clutch is not likely to be disengaged to the desired extent as soon as the wear upon the friction linings reaches a certain value. Thus, the distance which the bearing or bearings of the clutch operating apparatus should cover in response to repeated depression of the clutch pedal, in order to ensure that the positions of various parts of the clutch relative to each other do not change in response to repeated engagement and disengagement of the clutch, varies during the useful life of the clutch and the conventional operating apparatus therefor. In fact, the total play in the force-transmitting connection can rise to a value at which the aforementioned compensating mechanism is no longer capable of adequately compensating for wear upon the friction linings so that the engagement and/or disengagement of the friction clutch is no longer predictable. Thus, there exists an urgent need for clutch operating apparatus which are constructed and assembled in such a way that their operation is not affected by progressing wear upon certain components of the clutch and/or by progressing wear upon the constituents of the clutch operating apparatus.